The invention concerns a process and device for chassis control of suspension systems.
Known from the prior art are automotive systems which control or regulate the braking or acceleration processes of a vehicle in a fashion such that an optimum retardation, or braking, is assured while at the same time providing sufficient road stability.
The suspension systems between vehicle body and the wheels, as for the most still customary today, may be designed passive, that is with fixed damping and/or spring characteristic, or active, that is with variable damping or spring characteristic. While with the passive suspension systems it is necessary to accept compromises regarding the travel comfort and road safety, the active systems can be extensively adapted to the respective travel situations of the vehicle, so that in situations noncritical in terms of road safety a high travel comfort and in situations critical to road safety a high road safety is achieved.
In the articles "PKW-ABV-Bremssysteme mit weiteren integrierten Funktionen" [Passenger Car ABV Braking System with Further Integrated Functions] (Automobil-Industrie 5/89, pp. 659 through 673) and "Compound Control of Braking and Suspension Systems" (SAE paper 90 51 44, pp. 199 through 211), reference is made to the interactions between the actuations of the braking or propulsion control systems, for one, and the actuations of the suspension systems, for another. Specifically, these interactions are conditioned by the fact that the brake or propulsion control systems usually evaluate the RPM of the vehicle wheels. Detected by sensors, however, the RPM of the vehicle wheels--especially during a braking operation--are characterized by considerable disturbance modulations. Responsible as essential causes therefor are wheel footprint force fluctuations due to vertical stimulations. Furthermore, the article points out that due to the damping characteristic of the shock absorbers--which is differently designed for the traction and thrust stages--there is on time average a traction force generated which causes the vehicle body and the axles to approximate one another, i.e., causes the vehicle body to lower and thus simulate a greater load.
DE-OS 39 39 292 proposes a composite control system for automobiles which consists of an active or semiactive chassis control and antilock system (ABS) and/or drive slip control (ASR) components which jointly utilize sensors and evaluation and control circuits. Provisions for that purpose are that the evaluation circuits determine a safety level and that the control circuits emit, in contingence on the valuation of this safety level, control signals to the ABS/ASR components and the chassis control. Proposed here, specifically, is to always actuate the damping force adjustments during the ABS/ASR control phases in such a way that minimal wheel load fluctuations will occur.
DE-PS 38 37 863, moreover, describes a suspension system for vehicles where the adjustment of the shock absorbers is such that the difference between the damping coefficient for the traction stroke and the damping coefficient for the thrust stroke is varied. Due to the constant short-stroke vibrations of the wheels, caused by unevennesses of the road surface, the respective damper generates a force which acts upon the body and whose magnitude depends on the difference. With the damping coefficients different in the traction and thrust direction it is possible to generate resultant forces in one direction as the damper alternates in quick succession in the traction and thrust directions.
The problem underlying the present invention is to optimize the braking and/or acceleration processes by actuations of the suspension systems during the braking and/or accelerating maneuvers.